1. Field of the Invention
The present invention relates to a communication apparatus having a normal power consumption mode and a power saving mode and connected to a network via a network interface device.
2. Description of the Related Art
Heretofore, in image forming apparatuses, such as multifunctional peripherals or single-function printers, various schemes have been adopted to reduce power consumption. Among others, image forming apparatuses with a sleep mode (power saving mode) for consuming less power than in a standby state (normal power consumption mode) have become widespread.
In the sleep mode, power supply to the units of the image forming apparatus is stopped except to a random access memory (RAM), a network interface card (NIC), and an operation unit, so that power consumption during the sleep mode can be reduced to about 1 Watt (W) to a few W. During the sleep mode, an image forming process cannot be performed because during the sleep mode, power supply to the photosensitive drum and the fixing unit in the printer unit of the image forming apparatus is stopped, and also power supply to the central processing unit (CPU) and the hard disk drive (HDD) is stopped.
When a predetermined condition is met during the sleep mode, the image forming apparatus returns from the sleep mode to the standby state. The predetermined condition includes, for example, that (1) a user has operated the operation unit of the image forming apparatus, and that (2) the NIC has received a packet that meets the return condition from the sleep mode to the standby state. Thus, power is supplied to the operation unit or the NIC even during the sleep mode to check if any button is pressed on the operation unit or if the packet is received.
Packets that meet the return conditions include (1) a unicast packet addressed to the image forming apparatus, (2) a return packet to request a return from the sleep mode to the standby state, and (3) broadcast packets or multicast packets of a specific protocol. In other words, the return packet (2) denotes a magic packet that includes a particular pattern in the packet. The broadcast packets or multicast packets of a specific protocol (3) are search packets formatted according to a protocol to enable another node on the network to search for the image forming apparatus on the network.
In order to receive packets described above, the NIC of the image forming apparatus needs to be linked to the network also when the image forming apparatus is in the sleep mode. If the network standard is Ethernet®, for example, the NIC is linked in a communication mode previously specified or linked in a communication mode determined by using autonegotiation defined in IEEE802.1u. The communication mode mentioned here includes a link speed (communication speed) and a duplex mode (full duplex or half duplex).
The NIC in some recent image forming apparatuses supports a communication speed of 1000 Mbps (1 Gbps) in addition to the conventional speeds of 10 Mbps and 100 Mbps. However, in a communication mode of 1000 Mbps, the power consumption of the NIC is larger than that at 10 Mbps or 100 Mbps. Therefore, there is known a method for reducing power consumption in the sleep mode, which causes the NIC to behave as if it does not support 1000 Mbps during the shift from the standby state to the sleep mode and then causes the NIC to be linked back to the network.
It is possible to further reduce power consumption by selecting a low communication speed to suit the communication capability of the hub on the network from among communication speeds (10 Mbps and 100 Mbps) other than 1000 Mbps.
For example, Japanese Patent Application Laid-Open No. 2004-243533 discusses a method in which, when an image forming apparatus shifts to the power saving mode under the condition that the apparatus is connected to the hub, the media access control (MAC) unit of the image forming apparatus determines a communication speed in a manner to suit the communication capability of the hub.
Japanese Patent Application Laid-Open No. 2002-271334 describes a method in which, when communication has not taken place in the communication apparatus for a fixed period of time, the NIC connected to the host and the LAN changes the communication speed set in itself to a lower speed.
However, in a communication system in which the communication apparatus is connected to a network via the network interface device, consideration has not been taken for reduction of power consumption at the network interface device side when the communication apparatus is in the power saving mode.
More specifically, in Japanese Patent Application Laid-Open No. 2004-271334 mentioned above, since the image forming apparatus itself is directly connected to the network, attention has not been paid to a reduction of power consumption at the network interface device, which is independent from the image forming apparatus.
In Japanese Patent Application Laid-Open No. 2002-271334 described above, the NIC itself acts to reduce power consumption. However, when communication has not taken place in the NIC for a fixed period of time, the NIC discussed in Japanese Patent Application Laid-Open No. 2002-271334 changes settings of the communication mode in the NIC, but not in response to a command from another communication apparatus (the host).
As described above, in a system where the communication apparatus is connected to a network via the network interface device, power consumption cannot be reduced by the network interface device connected to the communication apparatus. Unless the network interface device itself incorporates some mechanism to reduce power consumption, power consumption by the network interface device cannot be reduced even when the communication apparatus enters the power saving mode.